At present, a wild-type cytochrome-c-containing GDH (CyGDH) and PQQGDH which uses pyrroloquinoline quinone as a coenzyme are used for self-monitoring blood glucose sensors. However, the wild-type CyGDH and PQQGDH have a drawback in that they are incapable of accurate measurement of the blood glucose level because they react not only with glucose, but also with xylose.
JP 2012-090563 discloses a mutant GDH having low reactivity with disaccharides, wherein mutations are present at positions 326, 365, and 472 in the α-subunit. However, its low reactivity has been shown only for maltose, and mutant GDHs having decreased reactivity with xylose or galactose have not been known.